Leptin replacement therapy does not improve the abnormal lipid kinetics of hypoleptinemic patients with HIV-associated lipodystrophy syndrome

Patients with HIV-associated dyslipidemic lipodystrophy (HADL) have characteristic lipid kinetic defects: accelerated lipolysis, blunted fat oxidation and increased hepatic fatty acid reesterification. HADL patients with lipoatrophy also have leptin deficiency. Small or non-randomized studies have suggested that leptin replacement improves glucose metabolism in HADL, with very limited data regarding its effects on the lipid kinetic abnormalities. We performed a randomized, double-blind, placebo-controlled, dose-escalating (0.02 mg/kg/d for two months; 0.04 mg/kg/d for a further two months) study of the effects of metreleptin on lipid kinetics in 17 adults with HADL, hypertriglyceridemia and hypoleptinemia. Rates of lipolysis, intra-adipocyte and intrahepatic reesterification and fatty acid oxidation were measured using infusions of (13)C(1)-palmitate and (2)H(5)-glycerol, and indirect calorimetry. Fasting lipid profiles and glucose and insulin responses to oral glucose challenge were also measured. Metreleptin treatment induced significant, dose-dependent increases in fasting plasma leptin levels. There was no significant change in total lipolysis, net lipolysis, adipocyte or hepatic re-esterification or fatty acid oxidation, or in fasting triglyceride or HDL-C concentrations, with metreleptin treatment. Metreleptin decreased fasting non-HDL-C levels (P<.01) and area-under-the-curve for glucose (P<.05). In hypoleptinemic HADL patients, treatment with metreleptin at 0.02 or 0.04 mg/kg/d does not improve abnormal fasting lipid kinetics, or triglyceride or HDL-C levels. Metreleptin does, however, improve glycemia and non-HDL-C in these patients. These results suggest a dissociation between leptin's effects on glucose metabolism compared to those on lipid kinetics in HADL.

Nutritional repletion of children with severe acute malnutrition does not affect VLDL apolipoprotein B-100 synthesis rate

VLDL apo B-100 is essential for the secretion of liver fat. It is thought that synthesis of this lipoprotein is impaired in childhood severe acute malnutrition (SAM), especially in the edematous syndromes, and that this contributes to the common occurrence of hepatic steatosis in this condition. However, to our knowledge, it has not been confirmed that VLDL apo B-100 synthesis is slower in edematous compared with nonedematous SAM and that it is impaired in the malnourished compared with the well-nourished state. Therefore, VLDL apo B-100 kinetics were measured in 2 groups of children with SAM (15 edematous and 7 nonedematous), aged 4-20 mo, at 3 stages during treatment. Measurements were done at 4 ± 1 d postadmission, mid- catch-up growth in weight, and at recovery (normal weight-for-length). VLDL apo B-100 synthesis was determined using stable isotope methodology to measure the rate of incorporation of (2)H(3)-leucine into its apoprotein moiety. The fractional and absolute synthesis of VLDL apo B-100 did not differ between the groups or from the initial malnourished stage to the recovery stage. Concentrations of VLDL apo B-100 were greater in the edematous than in the nonedematous group (P < 0.04) and did not differ from the initial stage to recovery. The data indicate that VLDL apo B-100 synthesis is not reduced when children develop either edematous or nonedematous SAM.

Effects of decreased availability of sulfur amino acids in severe childhood undernutrition

In studies of glutathione (GSH) metabolism in children with severe childhood undernutrition (SCU), slower erythrocyte GSH synthesis in children with edema was associated with lower concentrations of cysteine, the rate-limiting precursor of GSH synthesis. This finding suggested a shortage of cysteine available for GSH synthesis in children with edematous SCU. The plasma concentration of methionine, the sulfur donor for cysteine synthesis, was also lower in children with edematous SCU, suggesting decreased availability of methionine for cysteine synthesis. It is also possible that reduced methionine availability will result in decreased synthesis of S-adenosylmethionine, which could lead to an overall defect in methylation reactions. This review focuses on the relationship between cysteine availability and GSH synthesis in children with SCU. It also examines whether there is an inadequate supply of cysteine in those with edematous SCU and, if so, whether this is due to a shortage of methionine due to a decreased release of methionine from protein breakdown. Finally, the review explores whether a shortage of methionine results in decreased synthesis of S-adenosylmethionine, the universal methyl donor.

Restoration of impaired nitric oxide production in MELAS syndrome with citrulline and arginine supplementation

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most common mitochondrial disorders. Although the pathogenesis of stroke-like episodes remains unclear, it has been suggested that mitochondrial proliferation may result in endothelial dysfunction and decreased nitric oxide (NO) availability leading to cerebral ischemic events. This study aimed to assess NO production in subjects with MELAS syndrome and the effect of the NO precursors arginine and citrulline. Using stable isotope infusion techniques, we assessed arginine, citrulline, and NO metabolism in control subjects and subjects with MELAS syndrome before and after arginine or citrulline supplementation. The results showed that subjects with MELAS had lower NO synthesis rate associated with reduced citrulline flux, de novo arginine synthesis rate, and plasma arginine and citrulline concentrations, and higher plasma asymmetric dimethylarginine (ADMA) concentration and arginine clearance. We conclude that the observed impaired NO production is due to multiple factors including elevated ADMA, higher arginine clearance, and, most importantly, decreased de novo arginine synthesis secondary to decreased citrulline availability. Arginine and, to a greater extent, citrulline supplementation increased the de novo arginine synthesis rate, the plasma concentrations and flux of arginine and citrulline, and NO production. De novo arginine synthesis increased markedly with citrulline supplementation, explaining the superior efficacy of citrulline in increasing NO production. The improvement in NO production with arginine or citrulline supplementation supports their use in MELAS and suggests that citrulline may have a better therapeutic effect than arginine. These findings can have a broader relevance for other disorders marked by perturbations in NO metabolism.

Dietary cysteine is used more efficiently by children with severe acute malnutrition with edema compared with those without edema

BACKGROUND

Children with edematous severe acute malnutrition (SAM) produce less cysteine than do their nonedematous counterparts. They also have marked glutathione (GSH) depletion, hair loss, skin erosion, gut mucosal atrophy, and depletion of mucins. Because GSH, skin, hair, mucosal, and mucin proteins are rich in cysteine, we hypothesized that splanchnic extraction and the efficiency of cysteine utilization would be greater in edematous than in nonedematous SAM.

OBJECTIVE

We aimed to measure cysteine kinetics in childhood edematous and nonedematous SAM.

DESIGN

Cysteine flux, oxidation, balance, and splanchnic uptake (SPU) were measured in 2 groups of children with edematous (n = 9) and nonedematous (n = 10) SAM at 4.4 ± 1.1 d after admission (stage 1) and at 20.5 ± 1.6 d after admission (stage 2) when they had replenished 50% of their weight deficit.

RESULTS

In comparison with the nonedematous group, the edematous group had slower cysteine flux at stage 1 but not at stage 2; furthermore, they oxidized less cysteine at both stages, resulting in better cysteine balance and therefore better efficiency of utilization of dietary cysteine. Cysteine SPU was not different between groups but was ∼45% in both groups at the 2 stages.

CONCLUSION

These findings suggest that children with edematous SAM may have a greater requirement for cysteine during early and mid-nutritional rehabilitation because they used dietary cysteine more efficiently than did their nonedematous counterparts and because the splanchnic tissues of all children with SAM have a relatively high requirement for cysteine. This trial was registered at clinicaltrials.gov as NCT00069134.

Glucose and pyruvate metabolism in severe chronic obstructive pulmonary disease

The mechanisms leading to weight loss in patients with chronic obstructive pulmonary disease (COPD) are poorly understood but may involve alterations in macronutrient metabolism. Changes in muscle oxidative capacity and lactate production during exercise suggest glucose metabolism may be altered in COPD subjects. The objective of this study was to determine differences in the rates of glucose production and clearance, the rate of glycolysis (pyruvate production), and oxidative and nonoxidative pyruvate disposal in subjects with severe COPD compared with healthy controls. The in vivo rates of glucose production and clearance were measured in 14 stable outpatients with severe COPD (seven with low and seven with preserved body mass indexes) and 7 healthy controls using an intravenous infusion of [(2)H(2)]glucose. Additionally, pyruvate production and oxidative and non-oxidative pyruvate disposal were measured using intravenous infusions of [(13)C]bicarbonate and [(13)C]pyruvate. Endogenous glucose flux and glucose clearance were significantly faster in the combined COPD subjects (P = 0.002 and P < 0.001, respectively). This difference remained significant when COPD subjects were separated by body mass index. Pyruvate flux and oxidation were significantly higher in the combined COPD subjects than controls (P = 0.02 for both), but there was no difference in nonoxidative pyruvate disposal or plasma lactate concentrations between the two groups. In subjects with severe COPD, there are alterations in glucose metabolism leading to increased glucose production and faster glucose metabolism by glycolysis and oxidation compared with controls. However, no difference in glucose conversion to lactate via pyruvate reduction is observed.

Resting energy expenditure and protein turnover are increased in patients with severe chronic obstructive pulmonary disease

The mechanisms leading to weight loss in patients with chronic obstructive pulmonary disease (COPD) are poorly understood. Changes in protein metabolism and systemic inflammation may contribute to increased resting energy expenditure (REE) in COPD, leading to an energy imbalance and loss of fat and fat-free mass. The objective of this study was to determine first whether REE was increased in patients with COPD and, second, whether this was associated with increased protein turnover and/or systemic inflammation. Resting energy expenditure was determined using indirect calorimetry in 14 stable outpatients with severe COPD (7 with low and 7 with preserved body mass indices) and 7 healthy controls. Endogenous leucine flux, leucine oxidation, and nonoxidative disposal, indices of whole-body protein breakdown, catabolism, and synthesis, were measured using intravenous infusions of (13)C-bicarbonate and 1-(13)C-leucine. Total body water, from which fat-free mass and fat mass were calculated, was determined using an intravenous bolus of deuterated water. Plasma markers of systemic inflammation were also measured. As a group, subjects with COPD had increased REE adjusted for fat-free mass (P < .001) and faster rates of endogenous leucine flux (P = .006) and nonoxidative leucine disposal (P = .002) compared with controls. There was a significant correlation between REE and both endogenous leucine flux (P = .02) and nonoxidative leucine disposal (P = .008). Plasma concentrations of the inflammatory markers C-reactive protein and interleukin-6 were not different between COPD subjects and controls. Increased rates of protein turnover are associated with increased REE and loss of fat-free mass in COPD.

Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation

BACKGROUND

Aging is associated with oxidative stress, but underlying mechanisms remain poorly understood.

OBJECTIVE

We tested whether glutathione deficiency occurs because of diminished synthesis and contributes to oxidative stress in aging and whether stimulating glutathione synthesis with its precursors cysteine and glycine could alleviate oxidative stress.

DESIGN

Eight elderly and 8 younger subjects received stable-isotope infusions of [2H(2)]glycine, after which red blood cell (RBC) glutathione synthesis and concentrations, plasma oxidative stress, and markers of oxidant damage (eg, F(2)-isoprostanes) were measured. Elderly subjects were restudied after 2 wk of glutathione precursor supplementation.

RESULTS

Compared with younger control subjects, elderly subjects had markedly lower RBC concentrations of glycine (486.7 ± 28.3 compared with 218.0 ± 23.7 μmol/L; P < 0.01), cysteine (26.2 ± 1.4 compared with 19.8 ± 1.3 μmol/L; P < 0.05), and glutathione (2.08 ± 0.12 compared with 1.12 ± 0.18 mmol/L RBCs; P < 0.05); lower glutathione fractional (83.14 ± 6.43% compared with 45.80 ± 5.69%/d; P < 0.01) and absolute (1.73 ± 0.16 compared with 0.55 ± 0.12 mmol/L RBCs per day; P < 0.01) synthesis rates; and higher plasma oxidative stress (304 ± 16 compared with 346 ± 20 Carratelli units; P < 0.05) and plasma F(2)-isoprostanes (97.7 ± 8.3 compared with 136.3 ± 11.3 pg/mL; P < 0.05). Precursor supplementation in elderly subjects led to a 94.6% higher glutathione concentration, a 78.8% higher fractional synthesis rate, a 230.9% higher absolute synthesis rate, and significantly lower plasma oxidative stress and F(2)-isoprostanes. No differences in these measures were observed between younger subjects and supplemented elderly subjects.

CONCLUSIONS

Glutathione deficiency in elderly humans occurs because of a marked reduction in synthesis. Dietary supplementation with the glutathione precursors cysteine and glycine fully restores glutathione synthesis and concentrations and lowers levels of oxidative stress and oxidant damages. These findings suggest a practical and effective approach to decreasing oxidative stress in aging.

Phenylbutyrate improves nitrogen disposal via an alternative pathway without eliciting an increase in protein breakdown and catabolism in control and ornithine transcarbamylase-deficient patients

BACKGROUND

Phenylbutyrate is a drug used in patients with urea cycle disorder to elicit alternative pathways for nitrogen disposal. However, phenylbutyrate administration decreases plasma branched-chain amino acid (BCAA) concentrations, and previous research suggests that phenylbutyrate administration may increase leucine oxidation, which would indicate increased protein degradation and net protein loss.

OBJECTIVE

We investigated the effects of phenylbutyrate administration on whole-body protein metabolism, glutamine, leucine, and urea kinetics in healthy and ornithine transcarbamylase-deficient (OTCD) subjects and the possible benefits of BCAA supplementation during phenylbutyrate therapy.

DESIGN

Seven healthy control and 7 partial-OTCD subjects received either phenylbutyrate or no treatment in a crossover design. In addition, the partial-OTCD and 3 null-OTCD subjects received phenylbutyrate and phenylbutyrate plus BCAA supplementation. A multitracer protocol was used to determine the whole-body fluxes of urea and amino acids of interest.

RESULTS

Phenylbutyrate administration reduced ureagenesis by ≈15% without affecting the fluxes of leucine, tyrosine, phenylalanine, or glutamine and the oxidation of leucine or phenylalanine. The transfer of (15)N from glutamine to urea was reduced by 35%. However, a reduction in plasma concentrations of BCAAs due to phenylbutyrate treatment was observed. BCAA supplementation did not alter the respective baseline fluxes.

CONCLUSIONS

Prolonged phenylbutyrate administration reduced ureagenesis and the transfer of (15)N from glutamine to urea without parallel reductions in glutamine flux and concentration. There were no changes in total-body protein breakdown and amino acid catabolism, which suggests that phenylbutyrate can be used to dispose of nitrogen effectively without adverse effects on body protein economy.

Effects of rosiglitazone on abnormal lipid kinetics in HIV-associated dyslipidemic lipodystrophy: a stable isotope study

HIV-associated dyslipemic lipodystrophy (HADL) is a heterogeneous syndrome of fat redistribution, hypertriglyceridemia, and insulin resistance, associated with markedly accelerated rates of lipolysis, intraadipocyte and intrahepatic reesterification, and very low-density lipoprotein-triglyceride synthesis and release. The objective of the study was to determine if rosiglitazone can ameliorate these lipid kinetic defects in patients with HADL. Infusions of [(13)C(1)]palmitate and [(2)H(5)]glycerol were used to measure total and net lipolysis, adipocyte and hepatic reesterification, and plasma free fatty acid (FFA) oxidation in 9 men with HADL, before and after 3 months of treatment with rosiglitazone (8 mg/d). Rosiglitazone treatment significantly increased both total lipolysis (R(a) FFA(total) from 3.37 ± 0.40 to 4.57 ± 0.68 mmol FFA per kilogram fat per hour, P < .05) and adipocyte reesterification (1.25 ± 0.35 to 2.43 ± 0.65 mmol FFA per kilogram fat per hour, P < .05). However, there was no change in net lipolysis (R(a) FFA(net) 2.47 ± 0.43 to 2.42 ± 0.37 mmol FFA per kilogram fat per hour), plasma FFA oxidation (0.30 ± 0.046 to 0.32 ± 0.04 mmol FFA per kilogram lean body mass per hour), or FFA flux available for hepatic reesterification (0.59 ± 0.07 to 0.56 ± 0.10 mmol FFA per kilogram fat per hour). There were significant decreases in fasting plasma insulin concentrations and insulin resistance, but not in fasting plasma lipid or glucose concentrations. There was a significant decrease in waist to hip ratio (0.98 ± 0.02 to 0.95 ± 0.02, P < .05) consistent with a significant increase in hip circumference (0.93 ± 0.02 to 0.95 ± 0.02 m, P < .05), without change in waist circumference. Rosiglitazone significantly increased adipocyte reesterification and improved insulin sensitivity, but the potential benefit of these changes was compromised by increase in total lipolysis. Combining rosiglitazone with agents designed to blunt lipolysis could expand depleted peripheral adipose depots in patients with HIV lipodystrophy.

Rate of phenylalanine hydroxylation in healthy school-aged children

Hydroxylation of phenylalanine to tyrosine is the first and rate-limiting step in phenylalanine catabolism. Currently, there are data on the rate of phenylalanine hydroxylation in infants and adults but not in healthy children. Thus, the aim of the study reported here was to measure the rate of phenylalanine hydroxylation and oxidation in healthy school-aged children both when receiving diets with and without tyrosine. In addition, hydroxylation rates calculated from the isotopic enrichments of amino acids in plasma and in very LDL apoB-100 were compared. Eight healthy 6- to 10-y-old children were studied while receiving a control and again while receiving a tyrosine-free diet. Phenylalanine flux, hydroxylation, and oxidation were determined by a standard tracer protocol using oral administration of ¹³C-phenylalanine and ²H₂-tyrosine for 6 h. Phenylalanine hydroxylation rate of children fed a diet devoid of tyrosine was greater than that of children fed a diet containing tyrosine (40.25 ± 5.48 versus 29.55 ± 5.35 μmol · kg⁻¹ · h⁻¹; p < 0.01). Phenylalanine oxidation was not different from phenylalanine hydroxylation regardless of dietary tyrosine intake, suggesting that phenylalanine converted to tyrosine was mainly oxidized. In conclusion, healthy children are capable of converting phenylalanine to tyrosine, but the need for tyrosine cannot be met by providing extra phenylalanine.

Arginine flux, but not nitric oxide synthesis, decreases in adolescent girls compared with adult women during pregnancy

NO has been proposed as a mediator of vascular expansion during pregnancy. Inability to increase NO synthesis and/or production of its precursor, arginine, may contribute to pregnancy-induced hypertension. Adolescents have a higher incidence of gestational hypertension. It is not known whether pregnant adolescents can produce sufficient arginine to meet overall demands. Our objective was to measure and compare the arginine flux and NO synthesis rates of pregnant adolescents and adult women. Arginine, citrulline, and NO kinetics were measured by i.v. infusions of (15)N(2)-argininine and (2)H(2)-citrulline in 8 adolescents and 8 adult women in the fasted state at the end of the first and the beginning of the 3rd trimesters of pregnancy. Arginine flux decreased (P < 0.05) from trimester 1 to 3 in the adolescents but not in the adult women. NO synthesis rate did not change significantly in either group from trimester 1 to 3. In trimester 3, there was a positive association (r = 0.55; P = 0.02) between arginine flux and participants' age, indicating that flux was slower in the younger participants. These findings suggest that after a brief period of food deprivation, the pregnant adolescent cannot maintain arginine production like her adult counterpart in late pregnancy. This inability to maintain arginine production seems to be related to her younger age. It does not, however, affect her ability to synthesize NO in late pregnancy.

Glutathione synthesis is diminished in patients with uncontrolled diabetes and restored by dietary supplementation with cysteine and glycine

OBJECTIVE

Sustained hyperglycemia is associated with low cellular levels of the antioxidant glutathione (GSH), which leads to tissue damage attributed to oxidative stress. We tested the hypothesis that diminished GSH in adult patients with uncontrolled type 2 diabetes is attributed to decreased synthesis and measured the effect of dietary supplementation with its precursors cysteine and glycine on GSH synthesis rate and oxidative stress.

RESEARCH DESIGN AND METHODS

We infused 12 diabetic patients and 12 nondiabetic control subjects with [²H₂]-glycine to measure GSH synthesis. We also measured intracellular GSH concentrations, reactive oxygen metabolites, and lipid peroxides. Diabetic patients were restudied after 2 weeks of dietary supplementation with the GSH precursors cysteine and glycine.

RESULTS

Compared with control subjects, diabetic subjects had significantly higher fasting glucose (5.0 ± 0.1 vs. 10.7 ± 0.5 mmol/l; P < 0.001), lower erythrocyte concentrations of glycine (514.7 ± 33.1 vs. 403.2 ± 18.2 μmol/l; P < 0.01), and cysteine (25.2 ± 1.5 vs. 17.8 ± 1.5 μmol/l; P < 0.01); lower concentrations of GSH (6.75 ± 0.47 vs. 1.65 ± 0.16 μmol/g Hb; P < 0.001); diminished fractional (79.21 ± 5.75 vs. 44.86 ± 2.87%/day; P < 0.001) and absolute (5.26 ± 0.61 vs. 0.74 ± 0.10 μmol/g Hb/day; P < 0.001) GSH synthesis rates; and higher reactive oxygen metabolites (286 ± 10 vs. 403 ± 11 Carratelli units [UCarr]; P < 0.001) and lipid peroxides (2.6 ± 0.4 vs. 10.8 ± 1.2 pg/ml; P < 0.001). Following dietary supplementation in diabetic subjects, GSH synthesis and concentrations increased significantly and plasma oxidative stress and lipid peroxides decreased significantly.

CONCLUSIONS

Patients with uncontrolled type 2 diabetes have severely deficient synthesis of glutathione attributed to limited precursor availability. Dietary supplementation with GSH precursor amino acids can restore GSH synthesis and lower oxidative stress and oxidant damage in the face of persistent hyperglycemia.

Comparison of leucine and dispensable amino acid kinetics between Indian women with low or normal body mass indexes during pregnancy

BACKGROUND

Evidence suggests that in women with a normal to high body mass index (BMI; in kg/m(2)), the extra amino acids needed during pregnancy are met through reduced oxidation. It is not known whether a woman with a low BMI can make this adaptation successfully.

OBJECTIVE

The objective was to measure and compare leucine kinetic parameters and alanine-nitrogen, glutamine amide-nitrogen, and glycine and cysteine fluxes in Indian women with a low and normal BMI in early and midpregnancy.

DESIGN

Fasted- and fed-state kinetics were measured by infusing 1-[(13)C]leucine, [(2)H(2)]cysteine, [(2)H(2)]glycine, [5-(15)N]glutamine, and [(15)N]alanine in groups of 10 women with a low BMI (<18.5) and 10 women with a normal BMI (18.5-25) in the first and second trimesters of pregnancy.

RESULTS

Leucine, glutamine, glycine, and cysteine fluxes were faster in women with a low BMI in both trimesters, but there was no difference in alanine flux between groups. This difference was explained in the first trimester by a higher proportion of fat-free mass in low-BMI women. Leucine oxidation and percentage of dietary leucine oxidized were higher in low-BMI women in both trimesters, but nonoxidative disposal was not different between groups.

CONCLUSIONS

Although they use dietary protein less efficiently, low-BMI women maintain net protein synthesis at the same rate as do normal-BMI women and produce similar quantities of labile nitrogen for the de novo synthesis of other dispensable amino acids such as glycine and cysteine. The extra amino acids required for increased maternal protein synthesis during pregnancy are provided by an overall decrease in amino acid catabolism in women with normal or low BMI.

Comparing the glucose kinetics of adolescent girls and adult women during pregnancy

BACKGROUND

Fetal energy demands are met mostly from oxidation of maternally supplied glucose. In pregnant adults this increased glucose requirement is met by an increase in gluconeogenesis. It is not known, however, whether, like their adult counterparts, pregnant adolescent girls can increase gluconeogenesis-hence, glucose production.

OBJECTIVE

Our objective was to measure glucose kinetics in 8 pregnant adolescents and 8 adult women.

DESIGN

We measured glucose kinetics after an overnight fast by using a primed-constant 6-h U-(13)C-glucose infusion at the end of trimester 1 and early trimester 3.

RESULTS

From trimester 1 to trimester 3, whole-body glucose production increased significantly in both groups (P < 0.01). However, whereas the weight-specific rate in adults increased by 18.2%, it increased by only 14.3% in adolescents. In adults, the increase in whole-body glucose production was largely due to a significant increase (P < 0.01) in the rate of gluconeogenesis, but in adolescents there was no change in whole-body gluconeogenesis, and weight-specific gluconeogenesis actually decreased by 11.7%. In both groups, the rate of whole-body glycogenolysis increased significantly (P < 0.05) in trimester 3, and in adolescents, it increased by 95%.

CONCLUSIONS

These findings suggest that, in the fasted state in late pregnancy, pregnant adolescents cannot increase weight-specific glucose production by the same magnitude as their adult counterparts. Furthermore, whereas adult women increase glucose production primarily through gluconeogenesis, adolescents do so through glycogenolysis.

Glucose kinetics and pregnancy outcome in Indian women with low and normal body mass indices

BACKGROUND/OBJECTIVES

Fetal energy demands are met from the oxidation of maternally supplied glucose and amino acids. During the fasted state, the glucose supply is thought to be met by gluconeogenesis. Underweight women with low body mass index (BMI) might be unable to adequately supply amino acids to satisfy the demands of gluconeogenesis.

SUBJECTS/METHODS

Glucose kinetics were measured during the first and second trimesters of pregnancy in 10 low-BMI and 10 normal-BMI pregnant women at the 12th hour of an overnight fast using a primed 6 h U-(13)C glucose infusion and was correlated to maternal dietary and anthropometric variables and birth weight.

RESULTS

Low-BMI mothers consumed more energy, carbohydrates and protein, had faster glucose production (R (a)) and oxidation rates in the first trimester. In the same trimester, dietary energy and carbohydrate correlated with glucose production, glycogenolysis and glucose oxidation in all women. Both groups had similar rates of gluconeogenesis in the first and second trimesters. Glucose R (a) in the second trimester was weakly correlated with the birth weight (r=0.4, P=0.07).

CONCLUSIONS

Maternal energy and carbohydrate intakes, not BMI, appear to influence glucose R (a) and oxidation in early and mid pregnancy.

In vivo arginine production and nitric oxide synthesis in pregnant Indian women with normal and low body mass indices

BACKGROUND/OBJECTIVES

Nitric oxide (NO) has been proposed as a mediator of vascular expansion during pregnancy. Inability to increase NO synthesis and/or production of its precursor, arginine, may be a contributor to pregnancy-induced hypertension or preeclampsia. Because maternal weight is associated with blood pressure and risk of preeclampsia during pregnancy, it may also influence arginine and/or NO production. The purpose of this study was to determine the in vivo arginine production and NO synthesis rate in pregnant women with normal (n=10) and low (n=10) body mass indices (BMIs).

SUBJECTS/METHODS

Arginine flux and NO synthesis rate were measured in the postabsorptive state with constant infusions of 15N2-arginine and 13C,2H4-citrulline. Plasma concentrations of arginine and NO metabolites were also measured. Kinetic parameters were correlated to maternal variables, gestational age, birth weight and blood pressure.

RESULTS

Endogenous arginine flux was significantly faster in the low-BMI compared with normal-BMI women in the first trimester (63.1+/-3.4 vs 50.2+/-2.0 micromol/kg per h, P<0.01), but not in the second. Plasma NO concentration was higher (44.7+/-5.3 vs 30.4+/-1.9 micromol/l, P=0.03) and its rate of synthesis trended faster in the low-BMI compared with normal-BMI group in the second trimester. Maternal weight and BMI were negatively correlated with arginine flux in both trimesters and NO synthesis in the second trimester.

CONCLUSIONS

These findings suggest, but do not prove, that maternal BMI may be a factor in the ability to produce NO during pregnancy and may be one way by which BMI influences blood pressure during pregnancy.

Mucosal maltase-glucoamylase plays a crucial role in starch digestion and prandial glucose homeostasis of mice

Starch is the major source of food glucose and its digestion requires small intestinal alpha-glucosidic activities provided by the 2 soluble amylases and 4 enzymes bound to the mucosal surface of enterocytes. Two of these mucosal activities are associated with sucrase-isomaltase complex, while another 2 are named maltase-glucoamylase (Mgam) in mice. Because the role of Mgam in alpha-glucogenic digestion of starch is not well understood, the Mgam gene was ablated in mice to determine its role in the digestion of diets with a high content of normal corn starch (CS) and resulting glucose homeostasis. Four days of unrestricted ingestion of CS increased intestinal alpha-glucosidic activities in wild-type (WT) mice but did not affect the activities of Mgam-null mice. The blood glucose responses to CS ingestion did not differ between null and WT mice; however, insulinemic responses elicited in WT mice by CS consumption were undetectable in null mice. Studies of the metabolic route followed by glucose derived from intestinal digestion of (13)C-labeled and amylase-predigested algal starch performed by gastric infusion showed that, in null mice, the capacity for starch digestion and its contribution to blood glucose was reduced by 40% compared with WT mice. The reduced alpha-glucogenesis of null mice was most probably compensated for by increased hepatic gluconeogenesis, maintaining prandial glucose concentration and total flux at levels comparable to those of WT mice. In conclusion, mucosal alpha-glucogenic activity of Mgam plays a crucial role in the regulation of prandial glucose homeostasis.

Positive net movements of amino acids in the hindlimb after overnight food deprivation contribute to sustaining the elevated anabolism of neonatal pigs

During the neonatal period, high protein breakdown rate is a metabolic process inherent to elevated rates of protein accretion in skeletal muscle. To determine the relationship between hindlimb net movements of essential and nonessential amino acids in the regulation of hindlimb protein breakdown during an overnight fasting-feeding cycle, we infused overnight-food-deprived 10- and 28-day-old piglets with [1-(13)C]phenylalanine and [ring-(2)H(4)]tyrosine over 7 h (during 3 h of fasting and then during 4 h of feeding). Extraction rates for aspartate and glutamate after an overnight fast were 15% and 51% in the 10-day-old compared with 6% and 25% in the 28-day-old (P < 0.05) piglets, suggesting an altered requirement for precursors of amino acids to shuttle nitrogen to the liver as early life progresses. This occurred simultaneously with marginal positive hindlimb net balance of essential amino acids after an overnight fast, with negative net release of many nonessential amino acids, such as alanine, asparagine, glutamine, glycine, and proline. This suggests that newborn muscle does not undergo significant protein mobilization after a short period of fasting in support of an elevated rate of protein accretion. Furthermore, tyrosine efflux from hindlimb breakdown between overnight fasting and feeding periods was not different in the 10-day-old piglets, for which tyrosine was limiting, but when tyrosine supply balanced requirements in the 28-day-old piglet, hindlimb efflux was increased (P = 0.01). The results of the present study indicate that proteolysis and net movements of amino acids are coordinated mechanisms that sustain the elevated rate of net protein accretion during overnight feeding-fasting cycles in the neonate.